Pigment vehicle for coating materials



Patented Nov. 4, 1941 UHTE ()FFICE PIGMENT VEHICLE FOR COATING MATERIALSLloyd V. Casto, Detroit, Mich.

No Drawing. Application May 19, 1937, Serial No. 143,553

3 Claims. (c1. 134-49) The present invention is concerned withimprovements in decorative coatings, utilized in finishing variousarticles of manufacture generally at the source of manufacture thereofand is directed particularly to that class of coatings having metallicflake particles incorporated therein; such particles being commerciallyknown as bronzing powders. Powders of this type have been usedheretofore for pigmenting purposes, mixed with a suitable vehicle forobtaining surface finishes having a metallic appearance, such as that ofaluminum, bronze, etc. However, a characteristic of all such coatingmaterials is that a very substantial percentage of the metallic flakesmixed therein settles out of the vehicle, thus necessitating constantagitating during the period of application of the material to thearticle being coated.

As distinguished from prior practices, the present invention is directedto the provision of coating materials comprising metallic flakes and acoating vehicle which will oppose any leaflng action of the metallicparticles, the components of the vehicle being such that the particleswill remain suspended in the vehicle after the preparation thereof forconsiderable periods of time, and the particles will also remain insuspended condition in the vehicle when the vehicle is reduced with athinner to spray-gun consistencies at the time the coating material isto be consumed by the manufacturer.

A further purpose of my present invention is to derive an intermediatecompound, comprising a liquid carrier having metallic particlessuspended therein, and of known physical and chemical composition,adapted to comprise part of an ultimate coating material, wherebycertain optical effects of the metallic flakes upon the generalappearance of the finish or coating, can be controlled accurately.

I have determined that such an intermediate compound utilizable formixing with the ultimate coating material can be economically derivedthrough the use of either a nitrated cotton or a synthetic resin base insolution, when the particle size of the flakev material and the solvencyfactors of the liquid components of the vehicle are controlled.

For example, when a flake-suspending medium, comprising a low viscosity,nitro-cellulose base and a suitable solvent therefor, has introducedthereinto an aluminum flake pigment, ninety percent of the particles ofwhich have an average flake particle area not greater than 5x cm. andthe liquid and flake material are not be below certain limits.

thoroughly mixed, the flake particles will remain in suspension in theliquid without settling therefrom for substantial periods of time,insofar as industrial usage thereof is concerned.

When it is desired to utilize a flake carrier comprising a syntheticbase dissolved in a suitable solvent therefor, the materials selectedshould be such that the viscosity of the mix will The pigment flakesshould be thoroughly mixed therewith. It will be found that the flakematerial will remain in suspension at the time this intermediate carrieris added to the final vehicle, providing the viscosity of the finalcoating material is not reduced too low. An example of suitablesynthetic vehicle is disclosed in my co-pending application, Serial No.143,554, filed May 19, 1937.

It is understood that either of the foregoing intermediate vehicles forthe flake material will have mixed therein, subsequently, compatibledyes or coloring pigments for the purpose of obtaining the desired coloreflect in the ultimate coating; also, that other body media can be andusually are added to the intermediate coating mixture for the purpose ofobtaining other physical characteristics, such as determination ofdrying time, durability, hardness, etc.

Examples of the foregoing complete coatings respectively are as follows:

Example 1.Aluminum flake of a good commercial grade, in moist or pasteform, was introduced into a thinned liquid comprising a low viscositynitrated cotton base and a suitable solvent therefor, and this mixturewas stirred or agitated for several hours to bring about physicalseparation of the particles adhering to each other in clusters and alsoto remove any stearic acid remaining on the particles as the result ofthe mode of manufacture thereof. This mixture was then permitted tostand to permit a settling out of the heavier particles and the finerparticles were retained in suspension. The mixture with the suspendedparticles then was decanted or otherwise removed from the larger settledparticles.

The foregoing flake base was added to a lowviscosity nitrocelluloselacquer, dissolved in a suitable solvent compatible to the foregoingingredients and the resultant mixture comprised:

A transparent color was then added, the color being in solution and thesolvent therefor being compatible to mixing with the components of thestated compound. The coating can be thinned further withoutprecipitating any of the components thereof, providing the viscosity ofthe coating is maintained above thirty seconds when measured with a Fordcup viscometer number four orifice at 70 F.

Example 2.Aluminum flake was introduced into a mixture of mineralspirits and high-flash naphtha, there being 224 parts of the former, and56 parts of the naphtha. This material was subjected to constantagitation for a period of about six hours, whereby stearic acid carriedby the flake material, was removed from the flake particles and theflake particles were minutely separated from each other, therebyeliminating phys ical adherance of the particles in clusters. Thismixture Was then permitted to stand for a few hours, whereupon thecoarser flake particles settled out of the mixture and that portion ofthe mixture above the settled flake particles was removed. 218 parts ofa phenol modified alkyd resin dissolved in xylol (this mixture having asolid content of about fifty percent by weight), was then mixed with thecarrier having the aluminum flake particles suspended therein. Anydesired coloring matter compatible with the components of the foregoingcompound can then be added to the compound, and after a thorough mixingtherewith the coating material is ready for shipment. The compound canbe reduced with a thinner to a spray gun consistency,that

is, until its viscosity is reduced to about 39 seconds as measured in aFord cup viscometer number four orifice at 70 F., the thinning down, inthe example given, being effected by the use of a thinner comprising 224parts of mineral spirits and 56 parts of high-flash naphtha, to theextent of fifty percent.

It should be noted in the synthetic example given that at the time thecoating passes through the spray gun nozzle, the solids content of thecompound is reduced to about 12 (by weight) Without including the solidsfactor of the aluminum flakes particles.

Clear low viscosity nitrated cotton lacquers have about a 13% solidscontent at spraying gravity and about the maximum solids contentobtainable in nitrated cotton lacquers is from 32% to 33%. Highviscosity nitrated cotton lacquers (about 22 second cotton) will takeless maximum of pigment solids. Hence, it is apparent that the highviscosity nitrated cotton lacquers have a maximum solids limitationwhich is considerably less than the maximum solids limitation of a lowviscosity nitrated cotton lacquer at practical spraying consistencies.

It will be found that classes of materials of which the foregoingformulae are examples only, can be manufactured and used without causingthe settling or separation of the flake particles from the vehicle, anda surface coated therewith will have the desired color without adominating metallic appearance. Likewise, no leaflng effect will beapparent upon or near the surface of the coating.

A clear top coating or coating of clear lacquer can be applied over thepigmented coating for protective purposes and regardless of the colorselected in making up the final coating mixture, the coated surface willhave a subdued iridescent appearance.

It should be noted that the amount of solids given in the foregoingexamples are quite low. Nevertheless, the coating materials have a highsurface coating efficiency.

So-called bronze powders economically available, contain a highpercentage of flake particles having the degree of minutenesshereinbefore stated, and these particles can be segregated in apractical, economical way, in the following manner: Powders areavailable in the form of wet pastes, the moisture-maintaining mediumbeing chemically such as to be compatible to compounding or mixing withcoating material ingredients, such as a nitrated cotton base and asolvent therefor. Commercial flakes paste can be mixed by stirring thesame in such a solution and after permitting the mixture to stand forseveral hours, it will be found that practically all of the coarserparticles will have settled to the bottom of the mixture, while about90% of the finer particles, which have remained in suspension, will havean average area not greater than that hereinbefore defined. Preparationof the liquid with the suspended particles therein can be effected inany convenient way. Observation, by microscope, of a sample of thisintermediate liquid with the flakes suspended therein, will disclosethat the flake particles are in a dynamic suspension to a certainextent, and remain so for long periods of time, with only a small amountof settling of the flake particles after the initial settling of thelarger particles from the flake-suspending liquid. Hence, quantitles ofthis mixture can be prepared at one time. As stated, with thisintermediate mixture available, different coating materials, insofar ascolor and viscosity variations are concerned, can then be made by mixingtherewith transparent colors, plasticizers, thinners, etc., as may bedesired. As the coating congeals upon the surface being decorated, itsviscosity and density rise, thus holding the flake particles in randomrelationship throughout the coating cross-section.

Hence, final coating materials, prepared as described, will retain theflake particles in a suspended state, despite severe agitation duringthe drying period caused by the rapid volatilization of the solventtherefrom.

The foregoing disclosures are directed primarily to coating materialsutilizable for finishing sheet-metal products, but can be adapted towood, composition board, and other surfaces, as well as to use as aground coating in processes for obtaining finishes of the design type.

In prior patents and applications therefor, I

have set forth several developments directed to the so-called sheenefiect reproductions which are observable to the discerning eye in theappearance of finished natural woods, marbles, textiles, etc., and Ihave set forth the attainment of the reproductions thereof by the use ofvarious materials, such as an underlying base for an artistic design tobe applied thereon, in which precipitated salts of the halogen familyheld in suspension, fish-scale and metallic particles, are used. Whilethe halogen group of salts and the fish-scale, when used in a basecoating, will be compatible to color matching when incorporated in adesired coating vehicle, such as a lacquer base in a volatile solvent,nevertheless the use of ture will dominate the optical impressionimparted by such a surface. Observation under a microscope will reveal,however, that some metal particles are substantially uniformly visiblethroughout the ground coat surface, and the extent of particlevisibility can be varied, as described by varying the amount of theinital flake and carrier used. However, quantitative measurements of thelight reflecting, diffracting and diffusing factors of the decoratedsurface, when compared with a metallic surface, disclose that thedifiusion factor of a metallic surface is considerably less than saidcoated surface, and if a clear or transparent protective coating, whichhas about the same index of refraction as the body of the underlyingcoating (in the example given a protective coating of clearnitro-cellulose lacquer), is applied over said decorated surface, theamount of diffusely reflected light will be decreased. Usually theoptical properties of a base surface are dependent upon the degree ofroughness of the surface. However, for comparative purposes, I haveprepared a surfac with a coating, using fish-scale instead of aluminumflake, and find that while the coating with the fishscale prouces a finegrained surface, as compared to the said coated surface containing themetallic flake, nevertheless the optical properties of thelast-mentioned surface compare favorably with the fish-scale surface,due primarily to the presence of the highly reflecting aluminumparticles randomly distributed throughout said surface.

Optical tests also disclose that a surface decorated with the foregoingdescribed coating materials, (including aluminum flake particles of thesmaller sizes, insofar as aluminum flake materials of commercial formare concerned), will have the optical characteristic of changeability toa marked extent, and this characteristic is highly desirable in a groundcoating used in connection with an overlying transfer of a wood graindesign or other overlying artistic design simulating the tracery ofmarble, textiles, etc., the appearance of which has the opticalchangeability factor referred to. When a clear protectiv coating isplaced over the design transfer, this changeability characteristic ofthe ground coating becomes quite obvious between certain of thereflection angles of about 35 degrees to 60 degrees. A specularreflection is caused by the outer surface of the clear coating, as wellas those flake surfaces which are parallel to the outer surface, but adiffuse reflection is caused by other flake particles which isnon-metallic, due to the randomly distributed relationship of themajority of the flake particles, both on the base surface and below thebase surface, and this diffuse reflection is a combination of scatteringreflection and refraction caused by the randomly distributed particles.Hence, such a ground coating can have a matched color over which may beapplied an open tracery design in the form of a wood grain, a marble, atextile or any other reproduction of an article of commerce having acertain amount of sheen and changeability effect in the surfaceappearance thereof, as will b found, for example, in the appearance ofvarious walnut grains, mahogany grains, marbles, silks and othertextiles.

I have set forth in my prior Patent No. 2,047,- 670, and my priorapplications, Serial No. 34,034,

filed July 31, 1935, and No. 11,496, filed March 16, 1935, th obtainingof such final appearance results by the use of fish-scales, certaintypes of halogen salts, such as mercurous chloride, the use of metallicflake materials in the transfer inks, and the use of millbright metalbases. The results obtained by the use of the methods and materialsreferred to in said patent and patent applications are satisfactory, butin the instant case the use of a ground coating, having size controlledaluminum flake particles maintained in suspension therein, greatlysimplifies the manufacturing processes involved in obtaining the desiredresults.

It is to be understood, of course, that while I have given only twoexamples of a mixture and color for obtaining an ultimate coating notused in connection with a design tracery thereover, the amount of flakeparticles used in the coating and the coloring of the coating mixture,will vary in accordance with the manufacturers requirements.

When the decorated finish comprises a reproduction of the appearance ofa natural article, the ground coat color and sheen will be controlled tosimulate the dominating natural color and sheen of the article.

Where straight ground colored coatings are to be used with a clear,protective coating of lacquer or other clear coating placed thereover,such mixtures can be standardized and the completed coating materialsshipped for us at spray gun fluidities without any resulting settling ofthe flake particles from the coating material.

It is to be understood that, while I have given examples of the use ofintermediate flake carriers comprising in one instance an intermediatecarrier having a nitrocellulose base and in another a modified alkydresin base, the invention can be practiced by using an oil varnishsolution as an intermediate flake carrier, the adaptation of the same tothe foregoing described processes being apparent to anyone skilled inthe art in the light of the disclosures herein made.

I claim:

1. A ground coating composition comprising a colored vehicle including afilm forming material and non-leafing metallic flake, said metallicflake consisting of particles at least of which have an area not greaterthan .000,000,5 of a square centimeter and obtained by a processconsisting in agitating bronze powder with a liquid compatible with thebefore mentioned vehicle to thereby suspend the finer metallicv particleand permit the coarser particles to precipitate, and separating theliquid with the finer particles suspended therein from the coarserparticles; the

vehicle having a viscosity not less than 30 seconds, as measured with aFord Cup viscometer No. 4 orifice at 70 F., and saidparticles beingrandomly distributed in the colored vehicle and not appearing metallicupon casual observation when the coating material is applied to asurface to be decorated.

2. A coating material according to claim 1, wherein the vehiclecomprises a low viscosity nitro-cellulose lacquer and solvent therefor.

3. A coating material according to claim 1 wherein the vehicle includesa phenol modified alkyd resin.

LLOYD V. CAS'IO,

